Ferric caesium selenium alum, Cs₂SeO₄.Fe₂(SeO₄)₃

Ferric caesium selenium alum, Cs₂SeO₄.Fe₂(SeO₄)₃.24H₂O, prepared in an analogous manner to the preceding salt, yields violet crystals of density 3.6176 at 15° C. These melt in their combined water at 55° to 60° C.